A novel preparation, the amphibian cardiac ganglion, will be used to investigate the cellular basis of neuronal plasticity. The salient features of this preparation are (1) the tissue is very thin and individual ganglion cells, their processes, and even some synapses can be seen in the living isolated tissue, and (2) when some, but not all of the nerve terminals in the ganglion are destroyed by partial deafferentation, there is a striking reorganization, or sprouting, of the remaining intact synaptic terminals. Intracellular microelectrode recording will be combined with light and electron microscopy in order to correlate the structure and function of synapses during degeneration, sprouting, and regeneration. In particular, I propose to investigate in detail what initiates the sprouting of synaptic terminals, what is the functional significance of sprouting, and whether regenerating nerve terminals displace sprouted ones when they reinnervate the tissue. These results will be important not only for understanding how the vertebrate cardiac ganglion regulates the heart rate and how it can recover from damage, but can contribute fundamental information relating to what factors are important for maintaining synaptic connections in the nervous system.